1. Field of the Invention
This invention relates inter alia to artificial or modified natural blood-flow tubing, by which is meant artificial vascular prostheses or modified natural grafts or autografts, and tubing in which blood flows outside the body, e.g. in dialysis or in open heart surgery. Indeed, the invention might well extend to any tubing that carries a laminar flow, and particularly, but by no means exclusively, a pulsatile flow.
2. Description of the Related Art
Spiral flow has been observed (Stonebridge P. A. and Brophy C. M., 1991, Spiral laminar flow in arteries? Lancet 338: 1360-61) during angioscopy, as has the presence of spiral folds on the endoluminal surface of blood-vessels. The observation, it was said could have been an artifact of angioscopy, or the phenomenon may occur only in diseased arteries because of turbulence generated atherosclerosis, or it may be physiological, the latter having some support from other observations of rotational flow.
Indeed, in this seminal article, it is remarked that, if confirmed, the existence of spiral rather than laminar blood flow in peripheral arteries would have striking implications for the understanding of haemodynamics, arterial wall function, the pathogenesis of atherosclerosis and intimal hyperplasia, and the design of prosthetic graft materials.
Confirmation came with the publication by Stonebridge and others of a paper “Spiral laminar flow in vivo” in Clinical Science (1996, 9: 17-21) in which, using standard colour flow Döppler techniques, velocity information was obtained, from which a rotational element to forward flow during all or part of the pulse cycle was demonstrated in each of eleven healthy male volunteers.
However, even with this confirmation, it was admitted that it had not yet been shown whether angioscopic observations of a spiral pattern on the endoluminal surface of arteries and spiral flow patterns were real events or observational artefacts.
More recent work with magnetic resonance imaging (“MRI”) has established, however, that rotational flow is beneficial at least in certain situations and is presumed, on that account, to be “selected for”.
The prediction, therefore, by Stonebridge and Brophy in the 1991 Lancet report is vindicated, though it has only now become apparent just how to design prosthetic graft materials in order to reproduce, or at least not to destroy, the physiological rotation, and not at the same time bring about any disadvantages. It has also become apparent that the findings are of interest in connection with blood flow tubing other than grafts, and, indeed, with other tubing as well.